Inner Planet Basics

Mercury and Venus are the Solar System's innermost planets. Along with Earth and Mars, they also comprise the four terrestrial planets of the Solar System, with each having a solid planetary surface. Apart from a few physical characteristics, Venus is really nothing like the Earth and Mercury actually resembles Earth's Moon in many respects. Let's look at a few of the more important physical traits of these neighboring worlds.

Figure 9-2. The surfaces of Mercury and Venus.

At left, a Mariner 10 photomosaic of the Discovery quadrangle of Mercury (NASA/NSSDC).
At right, a Pioneer Venus Orbiter and Magellan map of the surface topography of Venus (light blue is lower, red is higher) showing the positions of Venrea probe landing sites (NASA).